1. Field of the Invention
The present invention relates to a mattress used for a nursing care bed and the like.
2. Description of the Related Art
Conventionally, in a part of a bed for supporting the human body, a mattress with a cushion function has been used to improve the comfort of sleeping by elastically supporting the human body. This type of mattress is made of elastic materials such as urethane foam, for example.
When a user, who has a difficulty in turning over in bed, continues to use a conventional mattress for a long period of time, reaction forces against the body pressure (due to the body weight) are exerted continuously on the user's body part, thus posing a risk of developing bedsores caused by interrupted blood circulation and the like. Therefore, in order to prevent bedsores from developing, a movable mattress is proposed that can disperse the reaction forces substantially applied against the body pressure of the user, by means of changing the working points of the user's body pressure through the use of fluid pressure. In other words, such a mattress has its working portion of the body pressure (that supports the human body) composed of multiple cells, wherein the cell heights are set to change at a prescribed timing by means of drawing fluid such as outside air into a fluid chamber of each cell and exhausting it therefrom to adjust the inner pressure of the cells. This causes the cells that substantially support the user's body and those that do not to interchange with each other at a prescribed timing, thus preventing the user's body parts from being compressed for a long time due to the body pressure. An example of such a mattress is explained in Publication of Japanese Patent No. 4494818.
However, in case of the movable mattress described in Japanese Patent No. 4494818 wherein the body supporting portion can be varied by periodical expansion and contraction of the cells, the user may be shaken on the mattress more than necessary to experience a discomfort feeling similar to sea sickness, which can cause nausea and vomiting, and that is why improved sleeping comfort has been sought for.
Also, Publication of Japanese Patent No. 2615206 describes a mattress that can bring its surface configuration in line with the body contour by controlling the cell heights for the purpose of dispersing the body pressure. It was considered that, using such a mattress, the user can prevent concentration of loads from working on the bulging parts of the user's body (e.g. buttocks), and at the same time, can avoid nausea and vomiting caused by a feeling of shaking.
However, the mattress described in Japanese Patent No. 2615206 is provided with a support member that connects cells with each other in order to keep each cell in a given direction, and deformation of the cells was too restricted to an approximately vertical direction to provide enough dispersion of the body pressure. In other words, the structure of the mattress described in Japanese Patent No. 2615206 had a risk of developing bedsores by concentrated body pressure around the contact portion between the outer periphery of the cells and the human body, for example, due to the surface configuration of the mattress capable of following the body contour having a curvy and smooth shape only in a series of steps.
In addition, deformation and displacement of the mattress surface in the planar direction is restricted by the mutual positioning of the cells by the support member in the planar direction of the mattress, which generates frictions between the user and the mattress surface when the user moves his body in the planar direction of the mattress, thus posing a risk of developing bedsores.